84 lines
2.4 KiB
C++
84 lines
2.4 KiB
C++
#include <union.h>
|
|
#include <iostream>
|
|
|
|
// This example shows how to use union relationships. Union relationships behave
|
|
// much like exclusive relationships in that entities can have only one instance
|
|
// and that adding an instance removes the previous instance.
|
|
//
|
|
// What makes union relationships stand out is that changing the relationship
|
|
// target doesn't change the archetype of an entity. This allows for quick
|
|
// switching of tags, which can be useful when encoding state machines in ECS.
|
|
//
|
|
// There is a tradeoff, and that is that because a single archetype can contain
|
|
// entities with multiple targets, queries need to do a bit of extra work to
|
|
// only return the requested target.
|
|
//
|
|
// This code uses enumeration relationships. See the enum_relations example for
|
|
// more details.
|
|
|
|
enum Movement {
|
|
Walking,
|
|
Running
|
|
};
|
|
|
|
enum Direction {
|
|
Front,
|
|
Back,
|
|
Left,
|
|
Right
|
|
};
|
|
|
|
int main(int argc, char *argv[]) {
|
|
flecs::world ecs(argc, argv);
|
|
|
|
ecs.component<Movement>().add(flecs::Union);
|
|
ecs.component<Direction>().add(flecs::Union);
|
|
|
|
// Create a query that subscribes for all entities that have a Direction
|
|
// and that are walking
|
|
flecs::query<> q = ecs.query_builder()
|
|
.with(Walking)
|
|
.with<Direction>(flecs::Wildcard)
|
|
.build();
|
|
|
|
// Create a few entities with various state combinations
|
|
ecs.entity("e1")
|
|
.add(Walking)
|
|
.add(Front);
|
|
|
|
ecs.entity("e2")
|
|
.add(Running)
|
|
.add(Left);
|
|
|
|
flecs::entity e3 = ecs.entity("e3")
|
|
.add(Running)
|
|
.add(Back);
|
|
|
|
// Add Walking to e3. This will remove the Running case
|
|
e3.add(Walking);
|
|
|
|
// Iterate the query
|
|
q.iter([&](const flecs::iter& it) {
|
|
// Get the column with direction states. This is stored as an array
|
|
// with identifiers to the individual states
|
|
auto movement = it.field<flecs::entity_t>(1);
|
|
auto direction = it.field<flecs::entity_t>(2);
|
|
|
|
for (auto i : it) {
|
|
// Movement will always be Walking, Direction can be any state
|
|
std::cout << it.entity(i).name()
|
|
<< ": Movement: "
|
|
<< it.world().get_alive(movement[i]).name()
|
|
<< ", Direction: "
|
|
<< it.world().get_alive(direction[i]).name()
|
|
<< std::endl;
|
|
}
|
|
});
|
|
|
|
// Output:
|
|
// e3: Movement: Walking, Direction: Back
|
|
// e1: Movement: Walking, Direction: Front
|
|
|
|
return 0;
|
|
}
|